Science

Yale scientists find a lone giant tortoise: the species was last seen more than 100 years ago

Evolutionary scientists are baffled by the 2019 discovery of a tiny female tortoise living on one of the Galapagos Islands' most remote islands. Scientists had previously found only one other tortoise of the species, a huge male found in 1906, once on Fernandina, an isolated island at the western end of the famous archipelago.

Yale scientists find a lone giant tortoise: the species was last seen more than 100 years ago

The 50-year-old turtle, which scientists named Fernanda, is closely related to a 20th century male specimen now preserved at the California Academy of Sciences, according to a Yale University study published in the journal Communications Biology. The discovery doubles the number of known members of Chelonoidis phantasticus.

However, this finding raises many new questions. Adalgisa Caccone, a senior research scientist and lecturer in the Department of Ecology and Evolutionary Biology at Yale University and senior author of the study, said, "A large number of genomes are similar between the two animals, but the processes that explain how this happened are unknown to us. This also shows the importance of using museum collections to understand the past."

According to the nonprofit Galapagos Conservancy, there are believed to be 15 different species of giant tortoises on the Galapagos Islands.

The new findings clearly show that the two giant tortoises found on Fernandina Island belong to their own lineage and are more closely related to each other than any other species of Galapagos giant tortoise. The population of these giant tortoises has declined by 85 to 90 percent since the early 19th century, mainly due to the arrival of whalers and pirates who killed them as food.

Yale scientists find a lone giant tortoise: the species was last seen more than 100 years ago

The discovery of a living specimen brings hope, but also opens up new questions, as many mysteries remain," Caccone said. Are there more turtles on Fernandina Island that could be brought back into captivity to start a breeding program? How did turtles colonize Fernandina, and what is their evolutionary relationship to other Galapagos giant tortoises?"

The turtles on Fernandina are thought to have been forced to extinction by volcanic eruptions on the island, including about 25 in the last two centuries. Scientists speculate that areas of vegetation were reduced by lava flows.

Galapagos National Park and the Galapagos Conservancy plan to look for close relatives of Fernanda on Fernandina Island in hopes of protecting the species, Caccone said, adding that the presence of other turtle droppings and tracks suggests they may find more animals on the island. If more turtles are found, conservationists could begin a captive breeding program, she said.

Deciphering the evolutionary relationship between these two Fernandina tortoises may be even trickier. First, they look very different. The male specimen has the large, prominent shell characteristic of saddleback terrapins, while Fernanda's shell is smaller and smoother, and Caccone suggests that this difference in shape may be due to stunting caused by limited food choices.

Yale scientists find a lone giant tortoise: the species was last seen more than 100 years ago

And, although the genomes of the two animals are very similar, the researchers found differences within the mitochondria, the part of the cell that produces energy that is transmitted through the mother. Because mitochondrial DNA is inherited from the mother, Caccone said it is possible that Fernanda is a hybrid species, descended from the male Chelonoidis phantasticus and the female C. nigra, a now-extinct species from Fernandina Island.

It is known that humans have moved different turtles, such as C. nigra, between the Galapagos Islands, including Isabela Island, where many hybrids between the endemic species C. becki and the extinct C. nigra were found. It is possible that a C. nigra female likewise found Fernandina and mated with a male of C. phantasticus, leaving its mitochondrial DNA to all its offspring.

Caccone believes that the males now housed in the California Museum may be true representatives of the original species. But to solve this new puzzle, she says, more tortoises from Fernandina need to be found.

Evolutionary biologists will be studying these and other questions in the coming years. "These turtles are the largest cold-blooded terrestrial herbivores on the planet and have a very important ecological role," Caccone said. "Therefore, it is important to conserve them, not only because of their iconic status, but also because they are an important agent of stability in the Galapagos ecosystem."

"There is still so much we don't know, and what we learn will provide guidance to help protect them and work with them to preserve the fragile and unique places on Earth they call home."